ID | MAIL
1  | no@gmail.com
2  | yes@gmail.com
3  | anything@gmail.com

SELECT * FROM TABLE
WHERE HashBytes('MD5', MAIL ) = 'CE42C51D0B63DF9F616CCFB4C3FCF16C'

CREATE INDEX mail_md5 ON TABLE(DECODE(MD5(MAIL), 'HEX'))